1. Field of the Invention
The present invention relates to a wireless communication system. More particularly, the present invention relates to an apparatus and method for estimating a channel in a wireless communication system.
2. Description of the Related Art
An Orthogonal Frequency Division Multiplexing (OFDM) transmission scheme based on multiple-carrier transmission has a 2 Dimensional (2D) structure in which signals are deployed in a symbol axis and a subcarrier axis, and pilots are also deployed according to the 2D structure. This structure has an advantage over other systems in terms of estimating a channel having a multi-path fading property. When estimating the channel, channel estimation capability is increased in proportion to the number of pilots, but as a result, the number of data signals is decreased relatively. Accordingly, the number of pilots that can be allocated is limited.
In the OFDM system, a receiving end first estimates a channel of a pilot tone, and then estimates a channel value of a data tone by using a channel estimation value. A Least Square (LS) scheme is used as a scheme of estimating the channel of the pilot tone. Linear interpolation, Low Pass Filter (LPF), Minimum Mean Square Error (MMSE), Wiener filtering, etc., are used as a scheme of estimating the channel of the data tone.
Linear interpolation is a scheme of estimating a channel value of a data tone by performing interpolation on a previously estimated pilot channel estimation value between adjacent values. Linear interpolation has an advantage in that a computational operation is simple and the complexity is small, but has a disadvantage in that channel estimation capability deteriorates when there is a significant change in a channel. Wiener filtering shows excellent performance, but has a disadvantage in that its complexity is high since it uses a process of obtaining a Wiener weight by performing an auto-correlation operation between pilots and a cross-correlation operation between data and a pilot.
Therefore, a high performance channel estimation scheme, such as Wiener filtering, is suitable when a channel environment has a fast fading property, and a simple channel estimation scheme, such as linear interpolation, is suitable when the channel environment changes slowly. Accordingly, there is a need for an apparatus and method for improving channel estimation capability by taking advantage of the two channel estimation schemes.